- ng-app mostly the name of the angular JS application.-The ng-app directive designates the root element of the application and is typically placed near the root element of the page.Example on <body> or <html> tag.-Only one ng-app per html document allowed.-AngularJS application cannot be nested withing each other

2.ng-model:

-ng-model directive binds the value of html controls such as input,selection,textarea to application data-registering control with its parents-provides validation behavior example:required,email,number,url or others

3.ng-bind:

-This will bind actual application data to html view means you can get input values from api and using ng-bind you can set that API data into html view.-you don't use ng-bind directly, but instead you use the double curly markup like {{ expression }} which is similar but less verbose.